Feature request: change z-order of type1000 layers after creating them

[btgoodwin]

Current behavior: the creation of the layer (e.g., overlay_pipe) establishes the z-order of the layer when drawing each layer.

What we would like to do is re-order layers in the event a signal on layer 1 needs to temporarily be displayed ahead of layer 0 (0 and 1 being indices into the layer list).